1. Field of the Invention
The present invention relates to a lens barrel which is provided with barrier blades disposed in the front of a photographic optical system, for protecting a photographic lens and openably covering a photographic aperture.
2. Description of the Related Art
A conventional lens barrel of the above-mentioned type is disclosed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. H07-159856.
The lens barrel is provided with a pair of barrier blades for openably covering a photographic aperture formed in the front of a photographic optical system, and the barrier blades are opened and closed by a barrier drive ring that rotates about the optical axis. A rotational force of a rotational barrel is transmitted to the barrier drive ring via a connecting shaft.
A barrier-closing spring is mounted between each of the barrier blades and the barrier drive ring. The barrier-closing spring always holds the associated barrier blade in contact with the barrier drive ring in a manner urging the barrier blade in the closing direction to thereby accommodate or absorb the motion of the barrier drive ring in a direction away from the barrier blades.
Further, between the barrier drive ring and a lens barrel cover, there is mounted a barrier-opening spring that urges the barrier drive ring to drive each of the barrier blades in the opening direction.
When the rotational barrel rotates in one direction, the rotational force of the rotational barrel is transmitted to the barrier drive ring via the connecting shaft, and the barrier drive ring rotates in the one direction while charging the barrier-opening spring.
At this time, each of the barrier blades is pressed by the associated barrier-closing spring to turn in the other direction according to the rotation of the barrier drive ring. As a consequence, the barrier blades are closed to cover the photographic aperture in the front of the photographic optical system.
On the other hand, when the rotational barrel rotates in the other direction, the rotational barrel is unhooked from the connecting shaft, and the barrier drive ring is rotated in the other direction by the charged spring force of the barrier-opening spring.
At this time, the barrier blades turn in the other direction according to the rotation of the barrier drive ring. As a consequence, the barrier blades are opened to open the photographic aperture in the front of the photographic optical system. Then, when fully opened, the barrier blades come into abutment with respective stoppers, whereby the pivotal motion of each of the barrier blades is restrained to stop the rotation of the barrier drive ring.
If some obstacle (e.g. foreign matter, such as sand) hinders the barrier blades from moving in the closing direction during their closing operation, the barrier-closing spring is charged by the barrier drive ring attempting to rotate in the one direction, whereby the rotation of the barrier drive ring in the one direction is allowed. In short, the barrier-closing spring permits the motion of the barrier drive ring in a direction away from the barrier blades. This prevents occurrence of a mechanical trouble.
As mentioned above, the lens barrel disclosed in Japanese Laid-Open Patent Publication (Kokai) No. H07-159856 requires the barrier-closing springs for accommodating the motion of the barrier drive ring away from the barrier blades when the motion of the barrier blades in the closing direction is blocked by some obstacle during the closing operation of the barrier blades.
For this reason, the two kinds of springs, i.e. the barrier-opening spring and the barrier-closing springs are required, which causes an increase in the number of component parts, resulting in increased manufacturing costs. Further, dedicated spaces for the barrier-closing springs are required, which hinders reduction of the size of the lens barrel.
Another problem is that the barrier drive ring is supported by being rotatably fitted on a shaft part, and between the barrier drive ring and the shaft part, there is created a radial clearance for ensuring smooth rotation of the barrier drive ring. Due to this arrangement, the barrier drive ring is always made eccentric from the shaft part by the urging force of the barrier-opening spring by an amount corresponding to the clearance, and hence when the pair of barrier blades operate to open or close the photographic aperture, a lag in timing for opening or closing the photographic aperture occurs between the operations of the respective barrier blades.
In such a case, if one of the barrier blades is fully opened and comes into abutment with the stopper to stop the rotation of the barrier drive ring, there can occur a problem that the other barrier blade is not fully opened.